An engine has a cooling apparatus for maintaining an engine temperature at an appropriate operating temperature. Commonly used cooling apparatuses include the apparatus that, by using a radiator, cools a coolant having a temperature that has increased inside the engine, and circulates the coolant through the engine, thereby cooling the engine. Such a cooling apparatus uses a method that does not circulate the coolant at the time of a cold start where the engine temperature is low, and circulates the coolant, when the engine temperature increases to a predetermined temperature. However, when no coolant flows inside the engine immediately after the cold start of the engine, a temperature distribution may occur inside the engine, leading to a stress or the like. Therefore, even when the engine temperature is low and the engine is not cooled by circulating the coolant, a very small amount of coolant is often allowed to flow inside the engine to avoid large unevenness in the temperature at various parts in the engine. For this purpose, a very small pore or a notch that allows the coolant to flow is often provided in a valve body in the cooling system.
In a cooling system with such a configuration, when the coolant does not flow due to foreign matter clogged in the pore or the notch, temperature unevenness may occur in the engine, leading to an increased stress and a reduced lifetime. Therefore, there has been proposed a method for estimating and determining clogging of the pore or the notch based on a difference in the coolant temperatures detected at different positions. In this case, one coolant temperature sensor is provided at an engine outlet and another one is provided in a bypass passage that bypasses the engine (for example, refer to WO 2013-150619).
Meanwhile, when no coolant has been injected in a cooling passage, or air remains in the cooling passage immediately after injection of the coolant, the cooling passage is not filled with the coolant. This may cause a failure in circulating the coolant by a coolant pump, and then the degree of increase in the coolant temperature at an engine outlet may be similar to a case when, there is clogging of a pore or a notch, leading to an erroneous determination of clogging of the pore or the notch.
Therefore, an object of the present invention is to suppress an erroneous determination of clogging of a pore that allows the coolant to flow in an engine cooling system.